When I search for on the Korean → Korean Naver Dictionary, some words have a number next to it.
What do those numbers mean?
In Korean, the same Hangeul characters can have multiple meanings. The number is there to distinguish between the different meanings. This is evident when you look at the search results for the same Hangeul.
P.S. Numbers are often used in other languages to represent tones, but Korean is not a tonal language.